Electroplating is a common process for depositing a thin film of metal or alloy on a workpiece article such as various electronic components for example. In electroplating, the article is placed in a suitable electrolyte bath containing ions of a metal to be deposited. The article forms a cathode, which is connected to the negative terminal of a power supply, and a suitable anode is connected to the positive terminal of the power supply. Electrical current flows between the anode and cathode through the electrolyte, and metal is deposited on the article by an electrochemical reaction.
Electroplating is widely used in the thin film head industry to fabricate magnetic and non-magnetic materials that constitute the writing part of a read-write head. Magnetic materials with Nickel and Iron are widely used as the write pole materials in thin film heads. Different compositions of nickel and iron provide different properties and hence are suitable for different applications.
For example, it is desirable to have a material with a large magnetic moment on both sides of the write gap, and materials of lower magnetic moment away from the write gap in order to prevent flux leakage that might cause interference on adjacent tracks of the media.
Thus, a preferred way of building a write head would involve bi-level deposition for both write poles, where material with a high magnetic moment positioned towards the write gap and material with a lower magnetic moment and higher resistivity is positioned away from the gap to reduce adjacent track interferences and eddy current losses, respectively.
It would also be desirable to perform the bi-level deposition from a single plating bath.
U.S. Pat. No. 5,489,488 discloses a process for making a soft magnetic multilayer film by a two step plating process that involves normal plating at the first step, and subsequently dissolving parts of the plated alloy and thereby forming a layer of different composition as the second step. One drawback of this approach is that the second layer is formed by dissolution and not deposition. This is significantly more difficult to control in terms of thickness and composition, because the amount and the relative frequency of dissolution is dictated by the inherent kinetics and not as much by the current. Also disadvantageous, the second layer (layer 7 in the disclosure) has to be significantly thinner than the first layer because of the above mentioned problem of thickness control, which gets worse as the dissolution duration increases.
Japan Patent No. JP6196324A discloses making laminates of different alloy films containing different compositions by changing current densities alone. The inventors use two direct current steps, one after the other in order to get the different compositions forming a sandwich layer. This current profile is then repeated to get repeat layers. However, using this direct current method, the composition range that can be achieved is very limited. The maximum composition range achieved has been 6% Fe (Ni81Fe19 to Ni87Fe13).
It would therefore be desirable to produce multiple layers of magnetic materials with varying composition from a single plating bath by changing the deposition conditions alone. It would also be desirable to create multilayers by deposition rather than dissolution, which provides significantly better thickness and composition control of the magnetic material. It would also be desirable to produce a bi-layer film with a composition range greater than those heretofore disclosed in the prior art.